The plastics (polyolefin) processing industry is constantly in search of means to improve the cost of manufacturing plastic articles. The cost of manufacture is influenced by a great many factors, but one of the major influences is cycle time. In the context of injection molding, cycle time refers to the time interval required to complete a single molding cycle and produce a single molded article. The molding cycle involves closing the mold, injecting molten plastic into the mold cavity, allowing the molten plastic to cool and partially solidify in the mold cavity, and ejecting the resulting part from the mold. The time required to complete the steps of closing the mold and ejecting the finished part from the mold are dictated by machine design. The steps of injecting the molten plastic into the mold cavity and cooling and solidifying the plastic are influenced by the properties of the polymer used in the process. For example, polymers having a relatively high melt viscosity cannot be rapidly injected into the mold cavity. Also, polymers having a relatively high melt viscosity typically must be heated to a relatively high temperature to ensure that they are sufficiently fluid to flow at the desired throughput and into the intricacies of the mold cavity. When a higher temperature is used, it takes longer for the molten polymer to cool to a temperature at which it is sufficiently solid for the part to be ejected from the mold cavity. (Heating the polymer to a higher temperature also requires greater amounts of energy, which increases the cost of the manufacturing operation and the cost of manufacturing each article.) Thus, in an effort to decrease cycle time and cost, the industry has begun to shift towards processes employing lower temperatures and polymers having lower melt viscosities. These lower melt viscosity polymers are capable of being fed through the processing equipment (e.g., passed through an extruder, injected into a mold cavity, etc.) at higher throughputs even at lower processing temperatures.
With this shift towards lower melt viscosity polymers and lower processing temperatures, the industry has discovered that some polymer additives do not function as expected or as desired. For example, in the case of clarifying agents, it has been found that Millad® 3988 clarifying agent (commercially sold by Milliken & Company) does not produce the same desirable low haze levels in low melt viscosity polymers as it does in higher melt viscosity polymer. This hindered performance can be problematic for a producer that wishes to lower cost by moving to a lower melt viscosity polymer while maintaining acceptable haze levels.
Thus, a need remains for additives, such as clarifying agents, which are suitable for use in lower melt viscosity polymers. A need also remains for polyolefin compositions containing such additives. The various embodiments described herein seek to provide such additives and compositions.